Two 2-phenyl-benzofurans, moracin C {2-[3',5'-dihydroxy-4'-(3-methlbut-2-enyl)phenyl]-6-hydroxybenzofuran} and its isomer iso-moracin C{2-[3',5'-dihydroxy-4'-(3-methlbut-1-enyl)phenyl]-6-hydroxybenzofuran}, were comparatively studied using redox-related antioxidant assays and non-redox antioxidant assays. Moracin C always resulted in higher IC50 values than iso-moracin C in the redox-related antioxidant assays, including •O₂--inhibition, Cu2+-reducing power, DPPH•-inhibition, and ABTS⁺•-inhibition assays. In the non-redox antioxidant assay, moracin C and iso-moracin C underwent similar radical-adduct-formation (RAF), evidenced by the peaks at m/z 704 and m/z 618 in HPLC-MS spectra. In conclusion, both moracin C and iso-moracin C can act as 2-phenyl-benzofuran antioxidants; their antioxidant mechanisms may include redox-related ET and H⁺-transfer, and non-redox RAF. A double bond at the conjugation position can enhance the redox-related antioxidant potential, but hardly affects the RAF potential.
Keywords: 2-phenyl-benzofuran; antioxidant; double bond; moracin; positional isomeric effect.